1. Field of the Invention
The present invention relates to devices for holding open hinged doors and covers of the type used for openings in roofs and floors.
2. Description of Related Art
Hatch covers, roof scuttles, floor doors and other types of openings in roofs and floors are provided with doors or covers that are hinged horizontally or at some angle to the vertical. The doors are typically heavy in order to support snow loads or traffic on their upper surface. Because such doors are heavy, and because the non-vertical hinging of the door would cause the heavy door to rapidly swing closed when released, all such doors need hold open arm assemblies to hold them open.
For safety, most such doors are counterbalanced, but even fully counterbalanced doors are usually provided with a hold open arm assembly. The hold open arm assembly prevents the door from suddenly closing-for example under the influence of a sudden wind gust, or by someone leaning or falling against the door. Another advantage of modern hold open assemblies for counterbalanced doors is that they can be operated to close the door with a single hand. This is an important safety feature for entry and exit openings having a ladder below the opening. Anyone climbing through the opening, to or from the ladder, must have one hand free to hold onto the ladder or railing to avoid a fall.
Prior art hold open arm assemblies have used a hold open arm with a perpendicularly protruding guide engaged in an elongated guide slot located in an arm guide bracket attached to the door. One end of the arm is hinged to the frame, and the guide, at the opposite end, slides in the guide slot. The guide slot has a width that matches the diameter of the guide and a notch at one end. When the door is opened, the guide drops into the notch to hold the door in the open position. A handle on the arm allows the user to swing the arm and pull the guide out of the locking notch. The guide moves along the guide slot and guides the door to the closed position.
Although hold open arm designs of the type described have been quite successful, one difficulty has been that the guide has served both the guiding function (to control the motion of the arm relative to the door) and the locking function (to prevent the door from closing unexpectedly). It has been difficult to design a guide with suitable properties for performing both functions. The load on the door can be quite high, particularly when the guide is preventing the door from closing under the unexpected application of a closing force. Thus, the guide is usually constructed of a material such as steel. This results in metal to metal contact between the guide and the guide slot. For smooth operation, it is preferred to eliminate this metal to metal contact.
Another disadvantage of earlier designs resides in the fact that the guide is offset from the longitudinal axis of the arm in order to engage the guiding slot. This offset means that when the guide is used to prevent the door from closing, the force resisting the closing force is also applied at a point offset from the longitudinal axis of the arm. This offset force application produces a significant bending moment on the arm when a large closing force is applied to the door. The resulting load on the guide may tend to damage the guide or bend the arm.
It is therefore an object of the present invention to provide a hold open arm assembly that has a smooth relatively frictionless operation, and yet which is extremely strong and resistant to closing forces applied directly to the door.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects, which will be apparent to those skilled in art, are achieved in the present invention which is directed to a hold open arm assembly for a non-vertically hinged door that includes an elongated arm having first and second ends, a handle attached to the arm for moving the door from an open position to a closed position, an arm guide bracket having a guide slot formed therein and a guide mounted to the second end of the arm and extending outward from the arm axis into guiding engagement with the guide slot. The first end of the arm is adapted for pivotal connection to a mounting surface and the second end has a stop surface thereon.
The arm guide bracket is mounted to the door and the guide slot defines a guide slot plane offset from the arm axis. A stop is mounted offset from the guide slot plane in approximate alignment with the arm axis when the door is in the open position. The stop contacts the stop surface on the arm and prevents motion of the door from the open to the closed position when a closing force is applied directly to the door.
The guide slot is preferably tapered to securely hold the guide at one end when the door is closed and allows motion of the guide perpendicular to the axis of the guide slot when the door is open. The perpendicular motion causes the stop to move into and out of engagement with the stop surface of the arm.
The stop surface is oriented at least ninety degrees relative to the guide slot axis. A bearing on the guide provides rolling contact between the guide and the guide slot. The bearing is non-metallic, preferably a tough plastic material such as nylon.
The guide may be a bolt extending perpendicular to the arm axis, with the bearing being mounted thereon. The stop may be a part of the guide bracket, comprising a tab bent perpendicular to the guide slot plane. To strengthen the arm, it may be stamped with a lengthwise strengthening ridge, substantially aligned with the arm axis.